There are many causes for back pain, including systemic disorders, tumors, and infections, but by far the most common cause is degenerative disease. This disease process is especially prominent in the lower lumbar spine, most commonly affecting the L4-L5 and L5-S1 levels.
A recent study from the American Chiropractic Society demonstrates that on average, 31 million Americans seek help for back pain annually. This number is growing for a number of reasons including, tobacco use, the increasing participation of Americans in contact sports and physical activity as well as the advancing age of American society. The vast majority of these patients are easily treated with conservative management such as Chiropractic adjustment, physical therapy, Massage therapy, and other techniques. However, a subset of patients with back pain will not respond to this type of treatment and are referred for surgical evaluation.
Much is yet to be learned in terms of the physiology and pathophysiology of the spine, and at present, a well-accepted paradigm is the so-called spinal motion segment. This refers to any particular pair of adjacent vertebrae along with the intervening disc and associated muscles, tendons, ligaments, and neurovascular structures. By evaluating any particular motion segment, thus better understanding the normal and abnormal movements at one level, one can better understood the spine as a whole, particularly when viewed as a series of adjacent motion segments rather than merely a vertically stacked series of vertebrae.
It is felt that one problem in degenerative disease is that there is excessive or abnormal movement between the vertebrae of one or more spinal motion segments. This is the basis for proposing surgical fusion, used for over 100 years now, which is a procedure in which the surgeon creates a milieu which encourages the development of a bony bridge between the vertebrae of a target motion segment, thus uniting these vertebrae into one large vertebra. Such a union would obliterate all movement at the target motion segment. Ultimately, approximately 400,000 patients annually undergo surgical fusion of the spine in the United States alone, with more than a million performed globally. These numbers have been fairly stable over the past decade.
Unfortunately, between 15 and 30% of such surgeries do not result in an outcome that the patient is satisfied with, and in fact a significant number of these patients report significant worsening of their symptoms. This syndrome, known as the so-called “failed back surgery syndrome,” or “post laminectomy syndrome,” is characterized by severe, chronic unrelenting pain which is poorly responsive to almost any intervention, as well as rather significant disability, and almost always associated with progressive severe depression and poor socialization. There are many thousands of such patients currently here in America, and this patient population creates an enormous drain on the health care delivery system. A system or device that would reduce this patient population would be of enormous value to the system.
Current technologies for establishing diagnoses all have shortcomings. Theoretically, the ideal patient who would optimally benefit from surgical fusion would be a patient who has a degenerative disease affecting a particular spinal motion segment in which it can be clearly shown that this spinal motion segment demonstrates an excessive I pathologic amount of movement, and that this movement is the genesis of the patient's pain—the so-called “pain generator.”
Despite the superb imaging and diagnostic tools which are now available to physicians and surgeons, demonstrating that this abnormal movement is unambiguously present, proving that this movement is responsible for at least the majority of the patient's symptoms remains remarkably challenging.
In addition to X-Rays and CAT scanning techniques, MRI scans have become the platinum standard for establishing diagnoses for the spine. But this has also been shown to have its shortcomings, principally in the fact that MRI studies demonstrate at times significant degenerative changes in patients that are asymptomatic. Therefore, identifying such changes in a patient who is symptomatic does not absolutely establish a causal relationship between the MRI findings and the patient's symptoms. This can sometimes lead to conclusions by both patients and surgeons, and sometimes results in such patients undergoing fusion surgery which does not relieve the patient's symptoms, and sometimes results in worsening of these symptoms.
This is because in additional to mechanical causes or pain—mechanical pain generators—there are other causes of back pain. It is well-known that there can be chemicals which are released locally which can lead to so-called “chemical pain generators. These may or may not be related to abnormal movements, so that stabilizing the spine with a fusion might, but is not guaranteed, to improve the pain.
Other issues that make back pain even more difficult to diagnose and treat include the fact that in many technologically-advanced countries, in particular the United States, back pain is frequently associated with injuries sustained in motor vehicle accidents, other injuries in which third parties are actionably responsible, or as the result of work related injuries. Such scenarios frequently result in litigation, resulting in the well-known phenomenon known as “secondary gain” causes of back pain. It is well documented that in many of these patients, only the favorable resolution of the associated litigation will result in a favorable resolution of the back pain.
A number of other pain generators have been identified or are alluded to, and added to that, it is well-known that back pain is a common complaint in patients who suffer from a phenomenon known as somatization disorder. This is a clinical situation in which a patient experiences and complains of back pain, and sincerely believes they are suffering from back pain, but ultimately the pain is not found to be related to any identifiable pathoanatomic or pathophysiologic derangement. It is important to recognize that this disorder is different and distinct from the “secondary gain” phenomena discussed above, nor it is related to malingering disorders or other issues in which the patient is cognizant that he or she is amplifying the symptoms; in somatoform disorder, the patient sincerely believes, in his or her soul, that he or she is suffering from some untreatable or rare disorder. Fusing such an individual will, without exception, result in disaster.
Therefore, sorting these issues out and determining who would be best served by a surgical fusion is ultimately more challenging than it may initially appear. The concept of “functional” MRI studies, which would demonstrate whether pain signatures are present on these specially-programmed MRI studies, has been proposed for some time now, and may help resolve some of these issues. While this may have significant value in years ahead, it is likely that this technology will have to undergo multiple scientific and legal challenges before it is fully accepted.
Another method which has been utilized, in one form or another, for many years in determining candidates for fusion surgery is discography. First introduced in 1948, this technique involves passing a needle into a target disc space and introducing X-Ray contrast into the disc space. The criteria by which the test is judged include the pressure required to inject the disc space, the radiologic appearance of the contrast as it flows into the disc space, and the symptoms reported by the patient at the time of the injection.
The value of discography has been a source of controversy for many years, and recently, has been under attack. Several studies have recently shown that injection of “normal” disc space can accelerate disc degeneration, and in fact, it is thought that this technique may precipitate degeneration in discs which may not have otherwise developed pathology.
Several basic science studies have suggested that passing a needle through the annulus fibrosus (the cartilaginous ring surrounding the outside of the disc) can—in and of itself—lead to disc degeneration; this is thought to be true even if nothing is actually injected into the disc space. This may be related to a humoral response to the insertion of the needle, with this humoral response triggering the degenerative process. If this can be shown to be unambiguously true, then this technique will likely be abandoned.
At one point, it was suggested that patients who might be candidates for fusion be placed in a back brace or possibly even a body cast to determine their response to stabilization. There are several problems with this approach. Firstly, there is good evidence that even a very secure body cast allows a significant amount of subtle movement between vertebrae, and does nothing to prevent microinstability from occurring. Secondly, it can be argued that prolonged periods (weeks to months) in a brace, and especially in a body cast (which cannot be removed by the patient) can have deleterious effects including a reduction of muscle tone (which itself can lead to back pain) as well as skin irritation such as blistering and contact dermatitis, generalized deconditioning of the soft tissues of the spine, and other problems. This host of issues often occurs, and added to that is the fact that such a device may not answer the critical questions: Is the patient's spine unstable? Is this instability the main cause of the patient's symptoms? And [ultimately] is fusion indicated?
Therefore, it remains necessary to develop a device and method which would allow a surgeon to transiently (over a period of a few weeks to several months) stabilize the spine in a manner that imitates the effects of a fusion. Such a device would, of necessity, have to provide immediate and secure stabilization
Such a device would stabilize a target motion segment in a fashion that would emulate a fusion, allowing the physicians attending to the patient to evaluate the patient's response to this type of stabilization over a period of time (weeks to months). In such a trial, if relief is reported, then the patient could be offered fusion. If the patient reported no improvement, or—of even greater importance—worsening of the symptoms, then the device could be removed and the patient would be informed that fusion should not be considered. Such a device would be unique, useful, novel and nonobvious.